1. Field of the Invention
The invention relates to a polyaxial bone anchoring device providing a pivot angle that is enlarged to one side compared to an opposite side. The polyaxial bone anchoring device comprises a bone anchoring element with a head and a shank and a receiving part for receiving a rod for coupling the rod to the bone anchoring element. The receiving part has two passages, each coaxial with a longitudinal axis, wherein the longitudinal axes of the two passages intersect one another and wherein one of the passages includes a seat configured to allow pivoting of the head. The head is insertable into the seat from a bottom end of the receiving part.
2. Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle to one side is known from U.S. Pat. No. 6,736,820 B2. This bone anchoring device comprises a screw member that is pivotably held in a receiving part, wherein the receiving part has an open first bore and a second bore on the end opposite to the first bore. On the bottom of the first bore, a seat for the head is provided. In order that the screw member can be pivoted to at least one side by an enlarged angle, an edge bounding the free end of the second bore viewed relative to the axis of the first bore is of asymmetric construction. The diameter of the second bore is greater than that of a threaded section of the screw member and smaller than that of the head.
Another bone anchoring device with an enlarged pivot angle is known from U.S. Pat. No. 6,974,460 B2. It includes a coupling element having an inner surface defining a first bore coaxial with a first longitudinal axis, and a second bore coaxial with a second longitudinal axis, whereby the second longitudinal axis intersects the first longitudinal axis. The coupling element has a seat adjacent to the lower end of the coupling element for the head of a bone anchoring element.
The polyaxial bone anchoring devices described above are top-loading anchoring devices wherein the anchoring element is inserted into the receiving part from an upper end thereof.
A bottom-loading polyaxial bone anchoring device is known from US 2011/0276098 A1. This polyaxial anchoring device comprises a rod receiving portion and a head receiving portion and an outer locking ring that is configured to compress the head receiving portion to clamp and finally lock the head. The anchoring element is insertable into the receiving part from a bottom end of the receiving part.